When running tests, installing operating systems, and compiling software for my Ultra 5, I came to the stunning realization that hey, this system is 64-bit, and all of the operating systems I installed on this Ultra 5 (can) run in 64-bit mode.

FYI, Solaris's ld (the dynamic linker) supports two entirely separate LD_LIBRARY_PATH variables for 32 and 64-bit executables. I would suggest that if you are going to mix executing the 64- and 32- bit binaries and need their respective dynamic libraries to get loaded automatically, read the manpage for ld. It was very helpful when I once wanted to do this.